As a sort of shock absorbers, a uni-flow type shock absorber is known in the art. For example, JP 2009-222136 A discloses a triple-tube structure uni-flow type shock absorber including an outer tube having a bottomed tubular shape, a cylindrical intermediate tube provided in an axial center portion of the outer tube in an upright manner, and a cylinder provided in an axial center portion of the intermediate tube in an upright manner.
The shock absorber includes a piston rod that accesses the cylinder, a piston held in a leading end portion of the piston rod and inserted movably along an axial direction inside the cylinder, and a base member fixed to the side of the cylinder opposite to the piston rod.
The inside of the cylinder is partitioned by the piston into a rod-side chamber and a piston-side chamber. A bottom chamber is provided between a bottom portion of the outer tube and the base member. A reservoir is provided in a cylindrical gap between the intermediate tube and the outer tube. The rod-side chamber, the piston-side chamber, and the bottom chamber are filled with working oil, while the reservoir is encapsulated with working oil and gas.
The piston is provided with a piston passage that allows only for a flow of the working oil directed from the piston-side chamber to the rod-side chamber. In addition, the base member is provided with an absorption passage that allows only for a flow of the working oil directed from the bottom chamber to the piston-side chamber.
The rod-side chamber communicates with the reservoir via a discharge passage including a through-hole formed in the cylinder and the cylindrical gap formed between the cylinder and the intermediate tube. The reservoir communicates with the bottom chamber via a notch formed in the base member. In addition, a damping valve for exerting resistance to the flow of the working oil passing through the discharge passage is provided in the middle of the discharge passage.
In this configuration, during both expansion and contraction operations of the shock absorber, the working oil moves to the reservoir via the same discharge passage. As a result, the shock absorber generates a damping force caused by resistance of the same damping valve during both the expansion and contraction operations.